1eye,
The AJ - 1515 RT that pops up first looks like a good start.
1.5 Watts and 1-3km line of sight distance should get you in the ball park.
The antennae are not much on gain. A decent directional antenna on the xmitter would most probable boost a bunch.
There ain't gonna be a free lunch on this idea. But the less you know about electronics the better chance you have of NOT over engineering the system.
I've heard that 1.5 Ghz range is not the best for some reason or another.
There are 802.11 jury rigged systems that range in miles.